Relation between Crystallite Size and Dispersion on Supported Metal Catalysts

Borodziński, Andrzej; Bonarowska, Magdalena

doi:10.1021/la962103u

Cited by 319 publications

(180 citation statements)

References 58 publications

(84 reference statements)

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“…The coating was studied by transmission electron microscopy (TEM) to investigate the Pd nanoparticle size distribution with the representative picture shown in Figure 3. The average diameter of the nanoparticles observed was 4.2 nm, which corresponded to a Pd dispersion of 28% using the calculation provided in reference [47]. …”

Section: Effect Of Liquid Flow Ratesmentioning

confidence: 94%

Process Intensification of Alkynol Semihydrogenation in a Tube Reactor Coated with a Pd/ZnO Catalyst

2017

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Semihydrogenation of 2-methyl-3-butyn-2-ol (MBY) was studied in a 5 m tube reactor wall-coated with a 5 wt % Pd/ZnO catalyst. The system allowed for the excellent selectivity towards the intermediate alkene of 97.8 ± 0.2% at an ambient H 2 pressure and a MBY conversion below 90%. The maximum alkene yield reached 94.6% under solvent-free conditions and 96.0% in a 30 vol % MBY aqueous solution. The reactor stability was studied for 80 h on stream with a deactivation rate of only 0.07% per hour. Such a low deactivation rate provides a continuous operation of one month with only a two-fold decrease in catalyst activity and a metal leaching below 1 parts per billion (ppb). The excellent turn-over numbers (TON) of above 10 5 illustrates a very efficient utilisation of the noble metal inside catalyst-coated tube reactors. When compared to batch operation at 70 • C, the reaction rate in flow reactor can be increased by eight times at a higher reaction temperature, keeping the same product decomposition of about 1% in both cases.

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Section: Effect Of Liquid Flow Ratesmentioning

confidence: 94%

Process Intensification of Alkynol Semihydrogenation in a Tube Reactor Coated with a Pd/ZnO Catalyst

2017

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“…In such catalytic processes as the steam reforming of ethanol (SRE) [2] or the Fischer-Tropsch synthesis (FTS) [3,4], besides operating conditions, the use of suitable catalyst plays a crucial role in achieving selective, efficient and economically profitable process [2,5,6]. The commonly used in the FTS or proposed for the SRE heterogeneous catalysts are cobalt-based ones [2][3][4][5][6][7], usually highly dispersed on inorganic oxide supports [8], which show a high activity and stability, relatively low cost and a high selectivity for the most desirable reaction products [9]. Among supports of the active phase, cerium oxide was used very often in various catalytic systems [3,10,11].…”

Section: Introductionmentioning

confidence: 99%

“…Dispersion (and the average size) of the metallic active phase is one of the most important parameters characterizing the heterogeneous catalysts [8], which are essential for the activity, selectivity and stability of catalytic processes. The catalytic activity of a supported catalysts depends on the degree of dispersion of the metallic active phase and its active surface area [8,18], and it usually increases with increasing dispersion of metal and decreasing its crystallites size [18]. On the other hand, the crystallites shape and their size distribution are important for mechanism of catalytic reaction, which dependents on the crystal faces exposed at the surface [19].…”

Section: Introductionmentioning

confidence: 99%

“…The crystallites size of metallic active phase are usually determined by hydrogen chemisorption, X-ray diffraction (XRD) or TEM (Transmission Electron Microscopy) [8,17,[20][21][22], but sometimes different results are found from various methods for the same catalyst. The differences in measurements of the crystallites size can result from methods limitation.…”

Section: Introductionmentioning

confidence: 99%

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Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

et al. 2016

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Cobalt catalysts with CeO 2 support, unpromoted and promoted with potassium were prepared by an impregnation method. Reduced catalysts were subjected to hydrogen chemisorption at different temperatures in the range of 313-453 K. Studies have shown that calculated Co crystallites size depends on the temperature of chemisorption. The average of size crystallites of the Co active phase obtained from the total and strong chemisorption data were compared with those from measurements by other techniques, TEM and XRD. The results of comparison allowed us to indicate the most suitable chemisorption temperature, different for unpromoted (383 K) and potassium-promoted (413 K) catalysts to determine the proper Co crystallites size of active phase, compatible with the crystallites size determined by the most objective method, i.e. by TEM measurements. In the case of small metal crystallites of active phase (4-5 nm) the divergence of their average size determined by hydrogen chemisorption and TEM methods and particularly by the XRD method is definitely higher than that in the case of larger crystallites (~12 nm).can significantly influence on obtained results. More than 40 years ago Bartholomew et al. [23][24][25] show that the chemisorption of hydrogen over cobalt catalysts with various supports (SiO 2 , Al 2 O 3 , C, MgO, ZSM-5, TiO 2 ) and over unsupported cobalt is activated and highly reversible. The activation was a function of the interaction of cobalt with a support or promoter. Frequently used in catalysis, potassium promoter significantly increased the adsorption activation energy for hydrogen [26]. It is also proved that some methods for determining the hydrogen uptake, i.e. flow adsorption methods such as thermal desorption and pulse methods, measure only irreversible (strong) chemisorption [23,27]. No hydrogen desorption was detected for MgOand ZSM-5-supported and low-loaded (1-3 wt.%) aluminasupported cobalt catalysts using TPD method, even though those catalysts adsorbed hydrogen when the static technique was applied [23,24]. The special case is the Co/TiO 2 system, where due to the strong metal-support interactions the stoichiometry of hydrogen chemisorption is lower than one hydrogen atom per surface cobalt atom, even in static measurements. With exception of the cobalt systems in which the strong metal-support interactions take place, the static technique was recommended for estimation of the average size of cobalt crystallites on the basis of maximal hydrogen chemisorption uptake, usually at 373 K. A good correlation with TEM measurements was found for the Co/SiO 2 , Co/γ-Al 2 O 3 and Co/C catalysts. The paper [9] also shows that the volume of chemisorbed hydrogen (including strong and weak chemisorption) on the CoRe/γ-Al 2 O 3 catalyst varies with the temperature of chemisorption, and the use of different data leads to the determination of different average size of crystallites, even though the actual crystallites size remains unchanged. They obtained the best results when the total chemisorption...

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“…These results mean that only insignificant part of the Pt atoms is exposed at the surface. Based on the relation between the crystallite size and dispersion on supported metal catalysts given by authors of work [37], platinum crystallite size was calculated. The results of these calculations show that the size of the platinum crystallite for the samples reduced at 50 and 100°C is similar & 8.5 nm, while for the samples reduced at 150 and 200°C, it is very large (70 nm).…”

Section: Platinum Dispersionmentioning

confidence: 99%

CO oxidation over Pt/SnO2 catalysts

Śmiechowicz

Kocemba

Rogowski

et al. 2018

Reac Kinet Mech Cat

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The influence of treatment conditions on Pt/SnO 2 properties and its catalytic activity in CO oxidation was investigated. It was found that the temperature and atmosphere of catalyst heating had a great impact on the active phase dispersion, the chemical composition of the surface layer and the O 2 adsorption capacity of the Pt/SnO 2 catalysts. TOF-SIMS analysis and XRD measurements showed that the heat treatment in an atmosphere of H 2 promotes the formation of bimetallic compounds of Pt-Sn and different species such as PtOH, PtO 2 , PtO 2 H, PtOCl, PtSnO, PtSnOH. It was stated that their presence significantly affects the activity of the catalyst in the CO oxidation. The catalyst capacity of O 2 adsorption varied depending on the treatment conditions. The catalyst treated at 600°C in oxygen showed the greatest ability of oxygen adsorption. A significant difference in the activities between the catalyst samples heated in O 2 or H 2 atmosphere was found. The highest activity was obtained for 1%Pt/SnO 2 sample treated in oxygen at 700°C. The treatment in hydrogen above 100°C caused a decrease in the catalyst activity.

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Relation between Crystallite Size and Dispersion on Supported Metal Catalysts

Cited by 319 publications

References 58 publications

Process Intensification of Alkynol Semihydrogenation in a Tube Reactor Coated with a Pd/ZnO Catalyst

Process Intensification of Alkynol Semihydrogenation in a Tube Reactor Coated with a Pd/ZnO Catalyst

Estimation of Average Crystallites Size of Active Phase in Ceria-Supported Cobalt-Based Catalysts by Hydrogen Chemisorption vs TEM and XRD Methods

CO oxidation over Pt/SnO2 catalysts

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